The Homogeneous Charge Compression Ignition engine is an engine of a system in which fuel is injected into a combustion chamber earlier or the fuel and a gas are mixed in an intake port and the premixed air-fuel mixture is caused to self-ignite in the vicinity of a compression dead center backed by a combustion reaction caused by a compression temperature, while a general diesel engine feeds by injecting the fuel in the vicinity of the compression dead center.
In the Homogeneous Charge Compression Ignition engine of this type, in order to obtain required output while ensuring a low NOx emission feature, it is necessary to suppress a combustion temperature determined by the heat value of the fuel and the heat capacity of the air-fuel mixture to a below temperature generating NOx. In other words, it is necessary that G/F being a ratio of an air-fuel mixture mass (fresh air+EGR gas) to a fuel mass is kept within a lean between 25 to 30 or more. Specifically, when the air-fuel mixture mass does not increase, the fuel supply amount is limited to increase, and as a result, it is impossible to increase a load to more than a half load of conventional engines (G/F=15).
Further, when a fuel injection amount is increased under the condition of a constant air-fuel mixture mass, a loud combustion noise arises caused by a pressure increase ratio due to a rapid temperature increase. This is also the cause not allowing the load increase by constraining G/F.
As a result, in a naturally aspirated (NA) engine limited to increase the air-fuel mixture mass, the higher limit of a high-efficient and super-low NOx HCCI operation zone is limited to about a half load of the conventional engines.
From a viewpoint of increasing the EGR ratio, there is one designed to increase the EGR gas amount introduced into the cylinder by slightly opening an exhaust valve simultaneously with the opening of an intake valve, in which the exhaust valve opening is affected by exhaust gas pulse of the other cylinder, to increase the EGR gas amount introduced into the cylinder (for example, see Nonpatent document 1).
[Nonpatent document 1] SAE20045094: Society of Automotive Engineers of Japan.